[openssl-users] Differences in openssl 0.9.8 and 1.0.1x for private pem key file

[Dave Thompson]

> From: openssl-users On Behalf Of Jaya Nageswar
> Sent: Monday, December 22, 2014 05:51

> In our application, we have been using openssl 0.9.8 and trying to move to 
> openssl 1.0.1x as 0.9.8 is going to be EOS by December 2015. We have a 
> sample application where we try to read a  sample pem key file, create an 
> EVP_PKEY indirectly using PEM_read_bio_PrivateKey [and] try to create 
> pem key files encrypted using different ciphers like (RC2, RC4 etc.). 
 
<snip lots of mechanism>

The mechanism was refactored some, but the visible change is deliberate.

There have long been routines for the algorithm-specific "traditional" 
formats PEM_read/write_RSAPrivateKey/DSAPrivateKey/ECPrivateKey 
AND for the newer standard and algorithm-generic PKCS8 format
PEM_read/write_PKCS8PrivateKey.

Through 0.9.8 PEM_write_PrivateKey used (the appropriate one of) 
traditional formats; in 1.0.0 and later it changed to use PKCS8. 
If you want to continue writing traditional formats in 1.0.0+ call 
specifically _write_RSAPrivateKey, _write_DSAPrivateKey, etc.
using the algorithm-specific struct from (instead of) EVP_PKEY.

At least for now; there is another thread started just a few days ago 
about all PEM formats used by OpenSSL suggesting the traditional
privatekey forms are obsolete and maybe should be deleted!

Note all PEM_read_xyzPrivateKey routines can read *either* 
format, legacy or PKCS8, distinguished by the BEGIN line, although 
if e.g. you _read_RSAPrivateKey and the file is PKCS8 for *another* 
algorithm that's an error; if you _read_PKCS8PrivateKey it accepts 
any algorithm into an EVP_PKEY.

If you are writing differently-encrypted privatekey files because 
you are concerned with key security, note one reason PKCS8
encrypted is preferred over traditional encrypted formats is
that PKCS8 allows and OpenSSL uses a much stronger PBE 
key derivation compared to the older and weaker but 
now set in stone and unchangeable one for traditional.

On checking I see the PEM_most manpage has not 
been updated for this change.